Were Republican senators out of bounds in sending a letter to Iran's government about the limits of President Barack Obama's power in foreign policy? That's what Vice President Joe Biden is saying.

Forty-seven senators sent the Iranian regime a letter -- first reported by Bloomberg View columnist Josh Rogin on Monday -- noting that the next president can abrogate any agreement that Obama makes with it over Iran's nuclear policy, and that they won't consider any agreement binding on themselves if Congress doesn't vote to approve it. Biden says the letter is "beneath the dignity" of the Senate, where he served for decades.

The conservative commentator Byron York says the senators' move is understandable, given the way the president has exceeded his legitimate powers, but still wrong: "It is not good to undermine the president's authority to conduct foreign policy."

I have some sympathy for Biden's view, even if it's not one he held when he was a senator undermining Republican presidents. The last few months have seen a troubling break with precedent in inter-branch relations over Iran policy. The administration has had a foreign leader call members of Congress to lobby them about a sanctions bill, and congressional leaders have had another foreign leader give an address rebuking the administration's policy. Both sides are using foreign officials to influence domestic political struggles.

This letter, though, raises less serious issues. For one thing, it doesn't convey any message that should come as a surprise to the Iranians. They were already presumably aware that Republicans (and some Democrats) don't like the shape of the deal that the administration wants to make with Iran. They also knew that most of the Republican presidential candidates have been critical of the administration's stance on the matter and promised to pursue a tougher policy if they win the 2016 election. Democrats have criticized the substance of the Republicans' position. But it would be implausible to say it’s wrong in principle for a presidential candidate to promise a new foreign policy. If presidential candidates can "undermine" a president’s policy, why can’t senators?

And anyway, it's not illegitimate, as Biden suggests, to "undermine the ability of any future American President, whether Democrat or Republican, to negotiate with other nations on behalf of the United States," or to conduct the foreign policy he favors. The Constitution itself undermines the president's power by giving Congress the right to declare wars, by letting it cut off funding for anything it chooses and by requiring the Senate's consent for treaties.

Some critics of the letter have pointed out that it may backfire. That is, it may send Iran the message that it is likely to get a better deal from this president than from the next one, and therefore make it more eager to conclude one now. Again, though, that's information the regime already has. The real question about the letter, then, isn’t whether it’s proper. It’s whether it accomplishes anything.

This column does not necessarily reflect the opinion of Bloomberg View's editorial board or Bloomberg LP, its owners and investors.

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